Substituted disulfides as antifoggants for silver halide emulsions



United Statesv Patent 3,057,725 SUBSTITUTED DISULFIDES AS ANTIFOGGANTSFOR SILVER HALIDE EMULSIONS Arthur H. Herz and Norman W. Kalenda,Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporationof New Jersey No Drawing. Filed July 17, 1959, Ser. No. 827,716 16Claims. (Cl. 96-109) This invention relates to the stabilization ofphotographic silver halide emulsions, and more particularly, to a methodof inhibiting development of spontaneous fog without adversely affectingthe sensitivity of the photographic silver halide emulsions.

It is well know that photographic emulsions on storage tend to losesensitivity and to become spontaneously developable without exposure tolight. There is norm-ally a detectable amount of the silver salt reducedduring development in the areas where no exposure was given; this iscommonly called fog, and sometimes called chemical fog where it isnecessary to distinguish between it and the effects of accidentalexposure to radiation; in this invention, we are not concerned with thelatter. Fog depends both on the emulsion and the conditions ofdevelopment; for a given emulsion it increases with the degree ofdevelopment. With constant development conditions, it tends to increasewith time, temperature and relative humidity of-storage conditions; itis common practice to make accelerated tests of the stability ofphotographic emulsions by storage at increased temperature or humidity,or both. It is, of course, desirable to have emulsions as stable aspossible under the conditions of high temperature and humidity which mayoccur in tropical climates, for example. Fog usually appears over thewhole area of the sensitive coating, but when severe, it frequently isnon-uniform. Fog may also be caused by exposure to chemicals, forexample, hydrogen sulfide and other reactive sulfur compounds, hydrogenperoxide vapor, and strongly reducing materials. While antifoggants andstabilizers may protect, to some extent, against such effects, it isnormally understood that antifoggants protect against spontaneous growthof fog during prolonged storage or storage at high temperatures andhumidities, or during development to maximum contrast and speed, orboth.

In emulsion technology, the use of certain organic disulfides aschemical sensitizers and stabilizers against incubation fog has beenpreviously described. Unfortunately, many of these disulfides haveproperties which place them in more than one of the above categories.For example, cystine is known to exhibit both sensitizing andantifoggant behaviour. In like manner, the disulfides obtained fromcertain mercapto carboxylic acids, such as those described in Matthieset al. U.S. Patent 1,742,042, issued December 31, 1929, have primarily asensitizing effect on photographic silver halide emulsions, with a muchless marked effect upon the stability of the emulsions.

Because of the above facts, the use of such organic di- I'sulfides asantifoggants, offers practical disadvantages.

Such disulfides having both sensitizing and some stabilizing activitycannot be employed in unsensitized or under- "ice ing photographicsilver halide emulsions without affecting to any material extent thesensitivity of the emulsions. Another object is to provide a method ofstabilizing both unsensitized and sensitized emulsions, withoutintroducing any substantial sensitizing or desensitizing effects. Stillanother object is to provide new organic disulfides and a method ofpreparation. Other objects will become ap parent from a consideration ofthe following description and examples.

According to our invention, photographic silver halide emulsions can bestabilized and the development of spontaneous fog substantiallyinhibited by incorporating therein certain organic disulfides.

The organic disulfides useful in practicing our invention comprisecompounds selected from those represented by the following generalformula:

wherein R and R each represents a methylene group (which may or may notbe substituted by hydrocarbon radicals, such as methyl, ethyl, phenyl,tolyl, etc., i.e., a hydrocarbon radical containing from 1 to 7 carbonatoms), m and n each represents a positive integer of from about 1 to 6and X and Y each represent a radical:

(B) -NRa (D) sR wherein R represents an alkoxy group (e.g., methoxyl,ethoxyl, etc.), an amine group (NI-I an alkylamino group (e.g.,methylamino, ethylamino, etc.), a dialkylamino group (e.g.,dimethylamino, diethylamino, etc.), or an -OM group wherein M representsa cation (.e.g., hydrogen, sodium, potassium, ammonium, p idinium,triethanolammonium, guanidinium, etc.), R" presents a hydrogen atom, analkyl group (e.g., me ethyl, propyl, isopropyl, butyl, etc.) or anaralkyl gro p"f(e.g., benzyl, ,B-phenylethyl, etc.), R represents anacyl group (e.g., an acyl group of a carboxylic or sulfonic acid, suchas acetyl, proponyl, butyryl, benzoyl, carbaniloyl, benzenesulfonyl,p-toluenesulfonyl, etc.), and R represents a hydrogen atom, analkylgroup (e.g., methyl, ethyl, propyl, etc.), an aralkyl group (e.g.,benzyl, fi-phenylethyl, etc.), or an acyl group, such as those listedabove forR, (R and R -n'1ay represent the same or difierent acylgroups).

Typical organic'disulfides embraced by the above general formulainclude, for example, the following:

KO S(CH -SS(CH SO K Potassium 3,3'-dithiodipropauesulfonate KO S-OHOHCHz-S SOHzOHzCHSO K Potassium 1,1'-d1methyl-3,3-dithlodipropanesulfonateor potassium 4,4J-dithiodi(2-butanesulfonate) (3) KO S(CH --SS(CH -SO K7 Potassium 4,4-dithiodibutanesulfonate (4) NaO S(CH S-S(CH -SO NaSodium 5,5-dithiodipentanesulfonate For the purpose of inhibiting fogformation, the disulfides of our invention can be added to the emulsionduring the process of manufacture in order to avoid loss of sensitivityand to inhibit the growth of fog with passage of time under nonidealconditions of storage.

An aqueous or organic solution of the disulfides of our invention whenadded at suitable concentration to unsensitized, chemically sensitized,or optically sensitized photographic emulsions does not appreciablyaffect the sensitometn'c values for sensitivity and fog whenmeasurements are made soon after coating. When sensitometricmeasurements are made at appreciable intervals of time, at elevatedtemperatures and dry or somewhat humid conditions, the disulfides of ourinvention do stabilize speed and maintain fog at a low level.

The preparation of silver halide emulsions involves three separations:(1) the emulsification and digestion or ripening of the silver halide,(2) the freeing of the emulsion from excess soluble salts, usually bywashing, and (3) the second digestion or after-ripening to obtainincreased sensitivity (Mees, The Theory of the Photographic Process(1942)). We prefer to add the fog-inhibiting agents after the finaldigestion r after-ripening, although they can advantageously be addedprior to digestion.

If desired, the disulfides of our invention can be incorporated in theemulsions without adverse effects by bathing techniques known to thoseskilled in the art.

The photographic emulsions used in practicing our invention are of thedeveloping-out type.

The emulsions can be chemically sensitized by any of the acceptedprocedures. The emulsions can be digested with naturally active gelatin,or sulfur compounds can be added such as those described in SheppardU.S. Patent 1,574,944, issued March 2, 1926; Sheppard et a1. U.S. Patent1,623,499, issued April 5, 1927, and Sheppard et al. U.S. Patent2,410,689, issued November 5, 1946.

The emulsions can also be treated with salts of the noble metals such asruthenium, rhodium, palladium, iridium, and platinum. Representativecompounds are ammonium chloropalladate, potassium chloroplatinate, andsodium chloropalladite, which are used for sensitizing in amounts belowthat which produces any substantial fog inhibition, as described inSmith and Trivelli U.S. Patent 2,448,060, issued August 31, 1948.

The emulsions can also be chemically sensitized with gold salts asdescribed in Waller et al. U.S. Patent 2,399,- 083, issued April 23,1946, or stabilized with gold salts as described in Damschroder U.S.Patent 2,597,856, issued May 27, 1952, and Yutzy and Leermakers U.S.Patent 4 2,597,915, issued May 27, 1952. Suitable compounds arepotassium chloroaurite, potassium aurithiocyanate, potassiumchloroaurate, auric trichloride and Z-aurosulfobenzothiazolemethochloride.

The emulsions can also be chemically sensitized with reducing agentssuch as stannous salts (Carroll U.S. Patent 2,487,850, issued November15, 1949), polyamines, such as diethyl triamine (Lowe and Jones U.S.Patent 2,518,698, issued August 15, 1950), polyamines, such as spermine(Lowe and Allen U.S. Patent 2,521,925, issued September 12, 1950), orbis(fl-aminoethyl)sulfide and its water-soluble salts (Lowe and JonesU.S. Patent 2,521,926, issued September 12, 1950).

The emulsions can also be optically sensitized with cyanine andmerocyanine dyes, such as those described in Brooker U.S. Patents1,846,301, issued February 23, 1932; 1,846,302, issued February 23,1932; and 1,942,854, issued January 9, 1934; White U.S. Patent1,990,507, issued February 12, 1935; Brooker and White U.S. Patents2,112,140, issued March 22, 1938; 2,165,338, issued July 11, 1939;2,493,747, issued January 10, 1950, and 2,739,964, issued March 27,1956; Brooker and Keyes U.S. Patent 2,493,748, issued January 10, 1950;Sprague U.S. Patents 2,503,776, issued April 11, 1950, and 2,519,- 001,issued August 15, 1950; Heseltine and Brooker U.S. Patent 2,666,761,issued January 19, 1954; Heseltine U.S. Patent 2,734,900, issuedFebruary 14, 1956; Van Lare U.S. Patent 2,739,149, issued March 20,1956; and Kodak Limited British Patent 450,958, accepted July 15, 1936.

The emulsions may also contain speed-increasing com- .pounds of thequaternary ammonium type of Carroll U.S.

Patent 2,271,623, issued February 3, 1942; Carroll and Allen U.S. Patent2,288,226, issued June 30, 1942; and Carroll and Spence U.S. Patent2,334,864, issued November 23, 1943; and the polyethylene glycol type ofCarroll and Beach U.S. Patent 2,708,162, issued May 10, 1955 and thethioether compounds of Graham and Sagal U.S. application Serial No.779,839, filed December 12, 1958, and the Dann and Gates U.S.application Serial No. 797,- 577, filed March 6, 1959.

The emulsions may contain a suitable gelatin plasticizer such asglycerin; a dihydroxy alkane such as 1,5-pentane diol as described inMilton and Murray U.S. application .Serial No. 588,951, filed June 4,1956; an ester of an ethylene bis-glycolic acid such as ethylenebis(methyl glycolate) as described in Milton U.S. application Serial No.662,564, filed May 31, 1957; bis-(ethoxy diethylene glycol) succinate asdescribed in Gray U.S. application Serial No. 604,333, filed August 16,1956, or a polymeric hydrosol as results from the emulsionpolymerization of a mixture of an amide of an acid of the acrylic acidseries, an acrylic acid ester and a styrene-type compound as describedin Tong U.S. Patent 2,852,386, issued September 16, 1958. Theplasticizer may be added to the emulsion before or after the addition ofa sensitizing dye, if used.

The emulsions may be hardened with any suitable hardener for gelatinsuch as formaldehyde; a halogen-substituted aliphatic acid such asmucobromic acid as described in White U.S. Patent 2,080,019, issued May11, 1937; a compound having a plurality of acid anhydride groups such as7,8-diphenylbicyclo(2,2,2)-7-octene-2,3,5,6-tetracarboxylic dianhydride,or a dicarboxylic or a disulfonic acid chloride such as terephthaloylchloride or naphthalene-1,5-disulfonyl chloride as described in Allenand Carroll U.S. Patents 2,725,294 and 2,725,295, both issued November29, 1955; a cyclic 1,2-diketone such as cyclopentane-l,2-dione asdescribed in Allen and Byers U.S.

'Patent 2,725,305, issued November 29, 1955; a bisester ofmethane-sulfonic acid such as 1,2-di-(methane-su1fonoxy)- ethane asdescribed in Allen and Laakso U.S. Patent 2,726,162, issued December 6,1955; 1,3-dihydroxymethylbenzimidazol-Z-one as described in July, Knottand Pollak U.S. Patent 2,732,316, issued January 24, 1956; a dialdehydeor a sodium bisulfite derivative thereof, the aldehyde groups of whichare separated by 2-3 carbon atoms, such as ii-methyl glutaraldehydebis-sodium bisulfite as described in Allen and Burness U.S. Patentapplication Serial No. 556,031, filed December 29, 1955; a bis-aziridinecarboxamide such as trimethylene bis(1-aziridine carboxamide) asdescribed in Allen and Webster U.S. patent application Serial No.599,891, filed July 25, 1956; or 2,3-dihydroxy dioxane as described in Jefi'reys U.S. Patent 2,870,013, issued January 20, 1959.

The emulsions may contain a coating aid such as saponin; a lauryl oroleyl monoether of polyethylene glycol as described in Knox and DavisU.S. Patent 2,83 1,7 66, issued April 22, 1958; a salt of a sulfated andalkylated polyethylene glycol ether as described in Knox and Davis U.S.Patent 2,719,087, issued September 27, 1955; an acylated alkyl taurinesuch as the sodium salt of N-oleoyl- N-methyl taurine as described inKnox, Twardokus and Davis U.S. Patent 2,739,891, issued March 27, 1956;the reaction product of a dianhydride of tetracarboxybutane with analcohol or an aliphatic amine containing from 8 to 18 carbon atoms whichis treated with a base, for example, the sodium salt of the monoester oftetracarboxybutane as described in Knox, Stenberg and Wilson U.S. Patent2,843,487, issued July 15, 1958; a water-soluble maleopimarate or amixture of a water-soluble maleopimarate and a substituted glutamatesalt as described in Knox and Fowler U.S. Patent 2,823,123, issuedFebruary 11, 1958; an alkali metal salt of a substituted amino acid suchas disodium N-(carbo-p-tert. octylphenoxypentaethoxy)glutamate asdescribed in Knox and Wilson U.S. patent application Serial No. 600,679,filed July 30, 1956; or a sulfosuccinamate such as tetrasodiumN-(1,2-dicarboxyethyl)-N-octadecyl sulfosuccinamate or N-lauryl disodiumsulfosuccinamate as described in Knox and Stenber U.S. patentapplication Serial No. 691,125, filed October 21, 1957.

The addenda which we have described may be used in various kinds ofphotographic emulsions. In addition to being useful in X-ray and othernonoptically sensitized emulsions they may also be used inorthochromatic, panchromatic, and infrared sensitive emulsions. They maybe added to the emulsion before or after any sensitizing dyes which areused. Various silver salts may be used as the sensitive salts such assilver bromide, silver iodide, silver chloride, or mixed silver halidessuch as silver chlorobromide or silver bromoiodide. The'agents may beused in emulsions intended for color photography, for example, emulsionscontaining color-forming couplers or emulsions to be developed bysolutions containing couplers or other color-generating materials,emulsions of the mixed-packet type, such as described in Godowsky US.Patent 2,698,794, issued January 4, 1955; or emulsions of themixed-grain type, such as described in Carroll and Hanson U.S. Patent2,592,243, issued April 8, 1952. These agents can also be used inemulsions which form latent images predominantly on the surface of thesilver halide crystal or in emulsions which form latent imagespredominantly inside the silver halide crystal, such as those describedin Davey and Knott U.S. Patent 2,592,250, issued April 8, 1952.

These may also be used in emulsions intended for use in diffusiontransfer processes which utilize the undeveloped silver halide in thenonimage areas of the negative to form a positive by dissolving theundeveloped silver halide and precipitating it on a receiving layer inclose proximity to the original silver halide emulsion layer. Suchprocesses are described in Rott U.S. Patent 2,352,014, issued June 20,1944, and Land U.S. Patents 2,584,029, issued January 29, 1952,2,698,236, issued December 28, 1954, and 2,543,181, issued February 27,1951; and Yackel et al. U.S. patent application Serial No. 586,705,filed May 23, 1956. They may also be used in color transfer processeswhich utilize the diffusion transfer of an image-Wise distribution ofdeveloper, coupler or dye, from a light-sensitive layer to a secondlayer, While the two layers are in close proximity to one another. Colorprocesses of this type are described in Land U.S. Patents 2,559,643,issued July 10, 1951, and 2,698,798, issued January 4, 1955; Land andRogers Belgian Patents 554,933 and 554,934, granted August 12, 1957;International Polaroid Belgian Patents 554,212, granted July 16, 1957,and 554,935, granted August 12, 1957; Yutzy U.S. Patent 2,756,142,granted July 24, 1956, and Whitmore and Mader U.S. patent applicationSerial No. 734,141, filed May 9, 1958.

In the preparation of the silver halide dispersions employed forpreparing silver halide emulsions, there may be employed as thedispersing agent for the silver halide in its preparation, gelatin orsome other colloidal material such as colloidal albumin, a cellulosederivative, or a synthetic resin, for instance, a polyvinyl compound.Some colloids which may be used are polyvinyl alcohol or a hydrolyzedpolyvinyl acetate as described in Lowe U.S. Patent 2,286,215, issuedJune 16, 1942; a far hydrolyzed cellulose ester such as celluloseacetate hydrolyzed to an acetyl content of 1926% as described in U.S.Patent 2,327,808 of Lowe and Clark, issued August 24, 1943; awater-soluble ethanolamine cellulose acetate as described in Yutzy U.S.Patent 2,322,085, issued June 15, 1943; a polyacrylamide having acombined acrylamide content of 3060% and a specific viscosity of0.25-1.5 on an imidized polyacrylamide of like acrylamide content andviscosity as described in Lowe, Minsk and Kenyon U.S. Patent 2,541,474,issued February 13, 1951; zein as described in Lowe U.S. Patent2,563,791, issued August 7, 1951; a vinyl alcohol polymer containingurethane carboxylic acid groups of the type described in Unruh and SmithU.S. Patent 2,768,154, issued October 23, 1956; or containingcyano-acetyl groups such as the vinyl alcohol-vinyl cyanoacetatecopolymer as described in Unruh, Smith and Priest U.S. Patent 2,808,331,issued October 1, 1957; or a polymeric material which results frompolymerizing a protein or a saturated acylated protein with a monomerhaving a vinyl group as described in U.S. Patent 2,852,382, ofIllingsworth, Dann and Gates, issued September 16, 1958.

If desired, compatible mixtures of two or more of these colloids may beemployed for dispersing the silver halide in its preparation.Combinations of these sensitizers, hardeners, etc., may be used.

The organic disulfides useful in practicing our invention can be addedto the photographic emulsions prior to the final digestion, if desired.Generally, these compounds can be added from a substantially neutralsolution so that the pH of the emulsion is not disturbed. In the case ofcompounds containing free sulfonic acid groups, this means that thesesulfonic acid groups may be at least partially neutralized. However,where it is desired to stabilize an acidic emulsion, it is obviously notnecessary that the antifoggant be added from substantially neutralsolutions. Since the disulfides of our invention can be added to theemulsions in such small quantities, it is apparent that they willgenerally have no adverse effect upon the pH of the emulsions. Many ofthe organic disulfides useful in practicing our invention can be addedto the emulsions in the form of substantially neutral aqueous solutions.If a particular'disulfide does not have sufiicient solubility in Water,addition to the emulsion can be made in the form of awatermiscibleorganic solvent, such as methanol, ethanol, dioxane, pyridine, etc. v l

The amount of disulfide compound added to the emulsions of our inventioncan be varied, depending upon the particular emulsion, the silver halidecontent of the emulsion, etc. In general, we have found that from about0.1 to 15.0 grams of disulfide per mole of silver halide canadvantageously be employed in our invention. One of the outstandingadvantages of the disulfides of our invention, as compared with thedisulfides which have been previously described in the prior art, isthat they can be used in quite substantial quantities withoutintroducing serious desensitizing eifects. Moreover, as indicated above,the disulfides useful in our invention advantageously have little or nosensitizing action of their own, and hence, they can be used tostabilize emulsions which have already been finished to their optimum ornear-optimum speeds. Thus, addition of our compounds to such finishedemulsions does not result in any substantial desensitizing effect, suchas might ordinarily be expected.

The following examples will serve to illustrate the useful stabilizingeffect of many of the organic disulfides useful in practicing ourinvention. A series of coatings was made on ordinary photographic filmsupport, such as cellulose acetate, of an ordinary photographichighspeed bromiodide emulsion, to which had been added one of theorganic disulfides of our invention at the concentration shown in thefollowing table. The compounds were added from substantially neutralsolutions and comparisons were made with an identical batch of emulsionwhich contained no antifoggant compound. After coating each series ofemulsions on a cellulose acetate support, the emulsions were dried andthen exposed on an intensity scale sensitometer (Kodak Type Ib) anddeveloped for about 4 minutes at 68 F. in a developer having thefollowing composition:

Cold water to make 1.0 liter.

Fresh tests and incubation tests (one week at 120 F., constant relativehumidity of about 50%, and in some cases for two weeks under the sameconditions) were also run for the same emulsion series with developmentunder the same conditions. The relative speed and fog for each of theseries coatings were then measured, the speed being determined at apoint about 0.3 density above fog.

In the following table the compound numbers correspond to the numbersused above for the specific disulfides. In each coating series, the sameemulsion batch was used, although difierent emulsion batches were usedfor some of the coating numbers identified in the coating table.Wherever a different emulsion batch was used, a new control series wasrun for that batch to show the degree of improvement obtained. Theresults of these coating series are given in the following table:

One Week Two Addendum Fresh Incubation Week Compound Test Test Incuba-Coating No. No. (g./ tion Test mol. AgX) Speed Fog Speed Fog Fog 1. None100 .08 139 22 62 1 (11. 4) 100 .09 136 .15 .48 3 (12. 3) 100 07 158 .11.25 2. None 100 13 87 31 66 2 (6. 3) 112 11 103 21 40 3. None 100 .17 9422 49 6 (1.1) 94 .16 83 .14 .16 7 (1.3) 107 14 105 .15 .22 4. None 10011 155 29 89 8 (0.48) 85 11 141 .21 .50 9 (1.2) 87 .09 162 .14 .40 9(3.0) 76 .10 132 .12 .29 5. None 100 17 82 25 49 (0. 72) 107 18 102 21The disulfides useful in stabilizing emulsions according to ourinvention can be obtained by methods which have been previouslydescribed in the prior art. For example, the disulfides of Formula IAcan be obtained by simple oxidation of the corrsepondingmercapto-substituted sulfonic acid or derivative. Oxidation canconveniently be accomplished by simply contacting the mercaptoderivative with an oxidizing agent, such as hydrogen peroxide, sodiumperchlorate, etc. The following examples will serve to illustrate thistechnique.

EXAMPLE A Potassium 3,3'-Dithiodipropanesulfonate Guanidinium3-mercaptopropanesulfonate (1 mol., 6.05 g.) was dissolved in 14 ml.water and passed through an Amberlite IR-120 (ion exchange resin) columnoperating in the acid phase. The column was washed with water (ca. ml.)until the eluate was neutral to indicator paper. The eluate, containing3-mercaptopropanesulfonic acid, was treated with 30% hydrogen peroxideA2 mol.+l2%, 1.8 g.) and allowed to stand at room temperature for 3hours. The solution was neutralized with aqueous potassium hydroxide,and water was removed in vacuo. The residue was washed well with etherand dried. After two recrystallizations from aqueous ethanol, the yieldof purified potassium 3,3-dithiodipropanesulfonate was 2.68 g. (49%).

Analysis.-Calcd. for C H O S K C, 18.6; H, 3.1; S, 33.2. Found: C, 18.7;H, 3.1; S, 33.6.

EXAMPLE B Potassium 4,4-Dithiodibutanesulfonate Guanidinium 4mercaptobutanesulfonate (1 mol., 7.00 g.) was dissolved in 15 ml. waterand passed through an Amberlite IR-120 column operating in the acidphase. The column was washed with water until the eluate was neutral toindicator paper. The eluate, containing 4-mercaptobutanesulfonic acid,was treated with 30% hydrogen peroxide /2 mol., 1.8 g.), and allowed tostand at room temperature for one day. The solution was neutralized withaqueous potassium hydroxide, and water was removed in vacuo. The residuewas stirred with ethanol, filtered oif, and dried. After tworecrystallizations from aqueous ethanol, the yield of purified potassium4,4'-dithiodibutanesulfonate was 4.36 g. (69% Analysis.-Calcd. forC8H1606S4K21 C, H, S, 30.9. Found: C, 23.1; H, 4.0; S, 20.6.

EXAMPLE C Potassium 4,4'-Dilhi0di(Z-Butanesulfonate) Guanidiuium4-mercapto-2-butanesulfonate (1 mol., 10.00 g.) was dissolved in ml.water and passed through an Amberlite IR- column operating in the acidphase. The column was washed with water until the eluate was neutral toindicator paper. The eluate, containing 4-mercapto-2-butanesulfonicacid, was treated with 30% hydrogen peroxide /2 mol., 2.5 g.) andallowed to stand at room temperature three days. The solution wasneutralized with aqueous potassium hydroxide, and concentrated in vacuoto a paste. The paste was stirred with ethanol, and the solid wasfiltered 011 and dried. After two recrystallizations from aqueousethanol, the yield of purified potassium4,4'-dithiodi(Z-butanesulfonate) was 5.53 g. (61%).

Analysis.Calcd. for C H O S K C, 23.2; H, 3.9; S, 30.9. Found: C, 23.7;H, 3.8; S, 31.0.

EXAMPLE D Guanidiuium 4,4-Dithi0di(2-Butanesulf0nare) Guanidiuium4-mercapto-2-butanesulfonate (1 mol., 5.00 g) was dissolved in 50 ml.water and the solution was made slightly alkaline with aqueous ammonia.A catalytic amount (ca. 0.05 g.) of ferrous sulfate was added, and adark brown solution resulted. The solution was stirred and gradually 30%hydrogen peroxide (/2 mol.+10%, 1.4 g.) was added. When addition wascomplete, the solution turned colorless. Iron hydroxides were filteredoff, and the filtrate was taken to near dryness in vacuo. The solid wasfiltered from a very small amount of water which remained, and dried.After two recrystallizations from methanolic chloroform the yield ofpurified guanidiniu-m 4,4-dithiodi(2-butanesulfonate) was 3.28 g. (66%),M.P. '231-3 C.

Analysis.--Calcd. for C H N O S C, 26.3; H, 6.2; S, 28.1. Found: C,26.3; H, 6.2; S, 28.2.

The 3mercaptopropanesu'lfonic acid salts and correspondingbmercaptobutanesulfonic acid salt were previously described by Schramm,Lemaire, and Karlson, JACS, 77, 6231 (1955).

The disulfides of Formula IB can be prepared by simply acylating thecorresponding amino compound. Acylation can be accomplished by merelycontacting the corresponding amino-disulfide with an acylhalide. In likemanner, the disulfides of Formula IC, wherein R represents an acylgroup, can be obtained by merely acylating the corresponding compoundsof Formula 1C, wherein R represents a hydrogen atom. Techniques ofacylation are well known to those skilled in the art and no particular'linowedge is required in order to acylate the amino orhydroXyl-substituted organic disulfides.

What we claim as our invention and desired secured by Letters Patent ofthe United States is:

l. A photographic silver halide emulsion stabilized with a water-solublecompound selected from the class consisting of those represented by thefollowing general formula:

wherein R represents an alkylene group having from 1 to about 6 carbonatoms and X represents a radical selected from the class consisting ofSO R and OR wherein R represents a member selected from the classconsisting of an alkoxyl group having from 1 to about 6 carbon atoms anda OM group wherein M represents a cation, R represents a member selectedfrom the class consisting of a hydrogen atom and an alkyl group havingfrom 1 to about 6 carbon atoms, R, represents an acyl group of anorganic acid selected from the class consisting of carboxylic acids andsulfonic acids, and R represents a member selected from the classconsisting of a hydrogen atom, an alkyl group having from 1 to about 6carbon atoms and an acyl group of an organic acid selected from theclass consisting of carboxylic acids and sulfonic acids.

2. A photographic silver halide emulsion stabilized with a water-solublecompound selected from the class consisting of those represented by thefollowing general formula:

wherein R represents an alkylene group having from 1 to about 6 carbonatoms, and R represents a member selected from the class consisting ofan alkoXyl group having from 1 to about 6 carbon atoms and a OM groupwherein M represents a cation.

3. A photographic silver halide emulsion stabilized with a water-solublecompound selected from the class consisting of those represented by thefollowing general formula:

wherein R represents an alkylene group having from 1 to about 6 carbonatoms, R represents a member selected from the class consisting of ahydrogen atom, an alkyl group having from 1 to about 6 carbon atoms, andR represents an acyl group of an organic acid selected from the classconsisting of carboxylic acids and sulfonic acids.

4. A photographic silver halide emulsion stabilized with a water-solublecompound selected from the class consisting of those represented by thefollowing general wherein R represents an alkylene group having from 1to about 6 carbon atoms and R represents a member selected from theclass consisting of a hydrogen atom, an alkyl group having from 1 toabout 6 carbon atoms, and an acyl group of an organic acid selected fromthe class consisting of carboxylic acids and sulfonic acids.

5. A photographic silver halide emulsion stabilized with a water-solublecompound selected from the class consisting of those represented by thefollowing general formula:

2 z( 2)m z)mz z wherein m represents a positive integer of from about 1to 6 and R represents a member selected from the class consisting of analkoxyl group having from 1 to about 6 carbon atoms and a OM groupwherein M represents a cation.

6. A photographic silver halide emulsion stabilized with a water-solublecompound selected from the class consisting of those represented by thefollowing general formula:

wherein m represents a positive integer of from about 1 to 6, Rrepresents a member selected from the class consisting of a hydrogenatom and an alkyl group having from 1 to about 6 carbon atoms and Rrepresents an acyl group of an organic acid selected from the classconsisting of carboxylic acids and sulfonic acids.

7. A photographic silver halide emulsion stabilized with a water-solublecompound selected from the class consisting of-those represented by thefollowing general formula:

wherein R represents an alkylene group having from 1 to about 6 carbonatoms and M represents a cation.

9. A photographic silver halide emulsion stabilized v with awater-soluble compound selected from the class consisting of thoserepresented by the following general formula:

wherein R represents an alkylene group having from 1 to about 6 carbonatoms and R represents an acyl group of an organic acid selected fromthe class consisting of carboxylic acids and sulfonic acids.

10. A photographic silver halide emulsion stabilized with awater-soluble compound selected from the class consisting of thoserepresented by the following general formula:

wherein R represents an alkylene group having from 2 to about 6 carbonatoms.

11. A photographic silver halide emulsion stabilized with awater-soluble compound selected from the class consisting of thoserepresented by the following general 14. A photographic silver halideemulsion stabilized formula: with 2,2-dihydroxydiethyldisulfide.

S 15. A photographic silver halide emulsion stabilized R50 (R) R5 with2,2-di(phenylcarbamyloxy)diethyldisulfide.

wherein R represents an alkylene group having from 2 5 A p gr ph ahalide ls n Stabilized to about 6 carbon atoms and R represents an acylgroup With 2,2'-di(benlenesulfonamidmdiethyldisulfideof an organic acidselected from the class consisting of carboxylic acids and sulfonicacids References Cited in the file of this patent 12. A photographicsilver halide emulsion stabilized UNITED STATES PATENTS with potassium3,3'-dithiodipropanesulfonate. 10 2,433,716 Mueller Man 1948 13. Aphotographic silver halide emulsion stabilized 2 440 20 Mueller APR 20,1948 with N,N-dibenzoyl-Z,2'-diaminodiethyldisulfide. 2,739,060 L et 120,

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION STABILIZED WITH A WATER-SOLUBLECOMPOUND SELECTED FROM THE CLASS CONSISTING OF THOSE REPRESENTED BY THEFOLLOWING GENERAL FORMULA: